1. Field of the Invention
The present invention relates to an electrostatic encoder which detects position information by the action of static electricity, and an electrostatic displacement measuring method.
2. Description of the Related Art
As a conventional apparatus to detect positions by the action of static electricity, there have been known an electrostatic capacity encoder disclosed in Jpn. Pat. Appln. KOKAI Publication No. 1-29409 and a capacitive position measuring transducer disclosed in Jpn. Pat. Appln. KOKAI Publication No. 4-67881 (U.S. Pat. No. 4,879,508). They have been commercialized as digital calipers. The digital calipers consume small electric power and can be driven with a battery. Thus, they have been widely used in workshops for accurately measuring the lengths of work pieces.
The basic principles of the apparatus disclosed in the above Jpn. Pat. Appln. KOKAI Publication No. 1-29409 and No. 4-67881 are the same. That is, many electrodes are arranged on a scale marked with graduations, and a plurality of transmitting and receiving electrodes is provided in a measuring unit opposite to the electrodes of the scale. The positional relationship between the scale and the measuring unit is measured by the phase of the received signal obtained by combining these electrodes.